Ways in which a valid written will may be revoked

Another will or codicil: this will or codicil must manifest the testators intention to revoke the previous will or codicil.
Destruction: this is the burning, leaving or otherwise destroying the will. The destruction must be coupled with an intention to revoke the will. (Cheese V. Lovejoy)
Marriage: the subsequent marriage of a testator revokes any will made, unless the will is made in contemplation of the particular marriage.